A waveguide is a structure that guides waves, such as electromagnetic waves or sound waves. Commonly known waveguides include hollow metal tubes which allow high frequency radio waves to “bounce” off walls of the hollow metal tubes to propagate down the waveguide. Commonly known waveguides have cross sections in rectangular, circular, or elliptical shapes. These common waveguides generally have a limited bandwidth, usually around 30% of a center of an operating frequency range.
Electromagnetic and sound waves in open space propagate in all directions as a spherical wave. When propagating in open space, the waves lose power proportional to the square of the distance from a source. When propagating in a waveguide, a wave has very little power loss, generally a wall conductor loss and a dispersive medium loss which are generally negligible. Ideally, the dimensions of a waveguide are selected so that, for a particular frequency(s), the wave is not cutoff and higher-order modes are not excited to minimize power loss.
One disadvantage of hollow metallic waveguides is the size of the waveguide. In general, the width of the waveguide needs to be of the same order of magnitude as the free-space wavelength of the guided wave. Thus, waveguides for radio and microwave transmission can be relatively large and unwieldy, especially when designed for frequencies in several hundreds or thousands of MHz range.
Accordingly, there is a need for an improved waveguide having smaller dimensions than an equivalent hollow metal waveguide at a particular operating frequency.